1 alert_click.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>alert from click</title>
</head>

<body>

    <a href="https://marketplace.visualstudio.com/items?itemName=ritwickdey.LiveServer"
        onclick="this.href=this.innerText">https://marketplace.visualstudio.com/items?itemName=ritwickdey.LiveServer</a>

    <ul>
        <li>function: alert()</li>
        <li>function declaration: button_onclick</li>
        <li>function: .querySelector()</li>
        <li>event type: click</li>
        <li>event handler assignment</li>
    </ul>

    <button id="button">click me</button>

    <script>
        // alert("message from alert");

        function button_onclick() {
            alert("click on the button");
        }
        document.querySelector("#button").onclick = button_onclick;
    </script>
</body>

</html>